EP1726919B1

EP1726919B1 - Method and apparatus for generating an origin signal of an encoder

Info

Publication number: EP1726919B1
Application number: EP06114414.3A
Authority: EP
Inventors: Kouichi Arai; Kazuhiko Kodama
Original assignee: Mitutoyo Corp
Current assignee: Mitutoyo Corp
Priority date: 2005-05-25
Filing date: 2006-05-23
Publication date: 2019-04-10
Anticipated expiration: 2026-05-23
Also published as: CN100549627C; JP2006329755A; US20060268379A1; JP4953589B2; US8130427B2; CN1869597A; EP1726919A1

Description

The present invention relates to a method and an apparatus for generating an origin signal of an encoder that has a scale on which an incremental pattern and an origin pattern are formed. In particular, the invention relates to a method and an apparatus for generating an origin signal of an encoder, by which the origin signal can be generated with high precision irrespective of origin waveforms obtained from the origin pattern.
Fig. 1 shows an encoder that obtains an incremental displacement signal (referred to as main signal) by using a scale 10 on which an incremental pattern 12 is formed. An origin pattern 14 is formed beside the incremental pattern 12 if it is necessary to acquire the point of origin on the scale 10. As shown in Fig. 2, an origin waveform is obtained from this origin pattern 14, and a pulsed origin waveform signal is then determined (see Japanese Patent Laid-Open Publications Nos. 2000-97726 , 2000-275063 , 2003-294494 , and 2004-163302 ).
In Fig. 1, the reference numeral 20 designates a detection head which includes a light source 22, an index scale 30, four main signal light-receiving devices 42, and an origin light-receiving device 44. The index scale 30 is provided with patterns 32 and 34 corresponding to the incremental pattern 12 and the origin pattern 14, respectively. The main signal light-receiving devices 42 acquire respective four phases of output for the sake of direction discrimination and phase division.
This method is highly tolerant to mounting and relative-Movement plays such as in the gap, arrangement, and orientation of the detection head 20 with respect to the scale 10. Nevertheless, the method also has had a problem of poor performances in use, including repeatability and bidirectionality.
In the meantime, encoders have improved in resolution and precision recently, and a demand for origin signals of higher precisions has become increasingly larger. It has thus been desired that the origin signals have resolution and precision equivalent to those of main signals, and be output in synchronization with the timing of the main signals as well. Japanese Patent Laid-Open Publication No. 2003-83771 describes the acquisition of an origin signal synchronous with a main signal.
Even with the technique described in Japanese Patent Laid-Open Publication No. 2003-83771 , however, it has been impossible to output an origin pulse that is adaptable to necessary origin pulse widths. In other examples, US-A-4970668 and EP-A-0453971 disclose encoders, the former for a crank angle sensor signal processor for an engine which is resistant against noise and the latter making use of a first and second track of non-identical non-complementary aperiodic patterns to generate a zero mark.
In view of the foregoing problems, various exemplary embodiments of this invention enable origin detection with excellent repeatability, S/N ratio (pulse width), and bidirectionality while maintaining ease of mounting and adjustment.
To solve the foregoing problems there is provided a method according to claim 1.
To solve the foregoing problems there is also provided an apparatus according to claim 2.
The apparatus may also comprise means for storing an origin position and the width of the origin signal detected by an initial operation after power-on.
The apparatus may also comprise: means for generating the origin signal in synchronization with the main signal waveform obtained from the incremental pattern.
According to the present invention, it is possible for users to set an origin point to a necessary position and width flexibly after power-on. Obtaining the origin signal of necessary width, it is therefore possible to secure a sufficient S/N ratio and establish a bidirectional origin.
More specifically, the origin track is actually detected in the first operation alone, while the origin signal is subsequently generated and output virtually by software. This solves the conventional problems that the origin slightly shifts in position each time it is detected, and that the origin signal varies in width. Since the origin signal is generated and output by software, it is also possible to preclude any positional shift of the origin signal regardless of whether the detection head is moving to the right or to the
left. Furthermore, it is possible to locate an origin with an arbitrary offset from the origin position detected by the initial operation, and then generate and output an origin signal each time the detection head passes that point (which achieves the function for free origin setting).
The origin detection essentially has to be performed only once at the beginning. In the meantime, numerical control (NC) units to be connected with the encoder have, by specifications, the function of checking the origin signal each time the origin is passed. Thus, if the origin signal is generated and output accordingly by software, it is possible to maintain compatibility with conventional encoders and resolve the positional shift of the origin signal as well. By using software, it is also possible to set the position and the width of the origin signal freely according to the specifications of the NC units.
In particular, when the rising edge of the scale origin is used as a slowdown watchdog signal (a trigger signal intended for a zero return operation) so that the rise of the origin or that of the origin inverted is put to subsequent use, it becomes possible to program the origin settings with a position and pulse width convenient for the system. This makes it possible to optimize (reduce) the zero return time.
Moreover, even if the scale is provided with a single origin alone, as shown in Fig. 3, it is possible to utilize the single origin as a slowdown watchdog while programming origin settings intended for zero coordinates to necessary positions.
As shown in Fig. 4, the origin outputs obtained from the actual origin and the zero coordinates can be ANDed to check for a miscount.
These and other novel features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments.
The preferred embodiments will be described with reference to the drawings, wherein like elements have been denoted throughout the figures with like reference numerals, and wherein;

Fig. 1 is a perspective view for explaining an origin detection unit of a conventional encoder;
Fig. 2 is a signal waveform chart for explaining the same;
Fig. 3 is an explanatory diagram showing the virtual output of an origin according to the present invention, for situations where the initial origin is used as a slowdown watchdog;
Fig. 4 is an explanatory diagram showing how to check for a system miscount according to the present invention;
Fig. 5 is a block diagram showing the configuration of an exemplary embodiment of the present invention;
Figs. 6A to 6C are waveform charts showing the operations of individual components according to the exemplary embodiment, for the case of a single-positioning origin; and
Figs. 7A and 7B are waveform charts for the case of a bidirectional-positioning origin.

Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the drawings.
As shown in Fig. 5, the present exemplary embodiment comprises a scale 10, a detection head 20, a phase division circuit 46, an internal counter 48, a waveform shaping circuit 50, and an origin signal generation circuit 52. The scale 10 has an incremental pattern 12 and an origin pattern 14. The detection head 20 includes an index scale 30 having an incremental pattern 32 and an origin pattern 34, a main signal light-receiving device 42, and an origin light-receiving device 44. The phase division circuit 46 divides the output of the main signal light-receiving device 42 in phase, thereby generating a main signal waveform having a signal pitch of, e.g., 10 µm as shown in Fig. 6A. The internal counter 48 counts up or down in accordance with the main signal waveform that is output from the phase division circuit 46. The waveform shaping circuit 50 shapes the waveform of the output from the origin light-receiving device 44, thereby generating an origin waveform (original waveform) such as shown in Fig. 6A. The origin signal generation circuit 52 is composed of programmable devices such as a CPLD. The origin signal generation circuit 52 is intended to generate and output, by software means, an origin pulse that rises in synchronization with the first zero crossing point of the main signal waveform within the range where the origin waveform obtained from the waveform shaping circuit 50 is on. Here, the origin pulse shall have a pulse width P as much as two pulses of the main signal, for example.
Hereinafter, the operation of the exemplary embodiment will be described. Initially, description will be given of the case with a single-positioning origin. When the detection head 20 moves to the right during an initial operation, the origin waveform and the main signal zero crossing point are synchronized into an output origin waveform, as shown in Fig. 6A. This output origin waveform, or pulsed origin waveform, is adaptable to a necessary origin pulse width P (in the diagram, as much as two pulses of the internal counter). As long as the power supply is on, the output origin waveform thereafter indicates an origin that is generated in the origin signal generation circuit 52 by software (referred to as software origin point), not in accordance with the actual signal but with the count value of the internal counter 48.
Then, when the detection head 20 moves to the left in the diagram, the origin pulse having the pulse width P is output by software in accordance with the DOWN pulses of the internal counter 48 as shown in Fig. 6B.
On the other hand, when the detection head 20 moves reversely to the right in the diagram, the origin pulse having the same pulse width P is output by software in accordance with the UP pulses of the internal counter 48 as shown in Fig. 6C.
In this way, the origin waveform is generated by software in accordance with the count value of the internal counter 48 irrespective of whether the movement is rightward or leftward. The origin waveform therefore remains unchanged in position and in pulse width.
Next, description will be given of the case with a bidirectional-positioning origin. When the detection head 20 moves to the right in the diagram, the origin pulse having the necessary pulse width P is output by software in synchronization with the rise of an UP pulse of the internal counter 48 as shown in Fig. 7A.
On the other hand, when the detection head 20 moves reversely to the left in the diagram, the origin pulse having the same pulse width P is output by software in synchronization with the rise of a DOWN pulse of the internal counter 48 so that it rises at the same position as the rising position of the above case as shown in Fig. 7B. Consequently, the origin waveform is obtained in the same position regardless of whether the detection head 20 is moving to the right or to the left.
It should be appreciated that in either of the cases with the single-positioning origin shown in Figs. 6A to 6C and the bidirectional-positioning origin shown in Figs. 7A and 7B, the counting direction of the detection head 20 is determined by the relationship between A and B phases of the analog waveforms obtained from the output of the main signal light-receiving device 42.
In the exemplary embodiment described above, the present invention is applied to an optical linear encoder of reflection type. Nevertheless, the present invention may be applied to linear encoders of ether types such as transmission type, magnetic type, electromagnetic induction type, and electrostatic induction type, and even rotary encoders.
When an incremental signal having necessary resolution can be obtained directly from the main signal light-receiving device 42, the phase division circuit 46 may be omitted.

Claims

A method of generating origin signals of an encoder having a scale(10) on which an incremental pattern(12) and an origin pattern(14) are formed,
the method comprising initially detecting the origin pattern and initially generating a first origin signal with preset width(P) at an origin position actually detected by an initial operation after power-on;
characterised in that the method further comprises
then generating following origin signals with the preset width(P) using software, the following origin signals being generated at positions of a predetermined count value of an internal counter (48) based upon a main signal waveform obtained from the incremental pattern and, in accordance with the obtained main signal waveform, DOWN pulses generated by movement in one direction relative to the incremental pattern causing the internal counter to count down and UP pulses generated by movement in an opposing direction causing the internal counter to count up, wherein the first origin pattern is actually detected in the first operation alone, and the following origin signals are subsequently generated virtually by software according to the count value of the internal counter (48).
An apparatus for generating origin signals of an encoder having a scale(10) on which an incremental pattern (12) and an origin pattern (14) are formed,
the apparatus comprising:
means for obtaining an origin waveform from the origin pattern(14);

means for obtaining a main signal waveform form the incremental pattern (12);

means for generating a first origin signal with preset width(P) at an origin position actually detected by an initial operation after power-on;
an internal counter (48) for counting the main signal waveform and outputting a count based upon a main signal waveform obtained from the incremental pattern and, in accordance with the obtained main signal waveform, DOWN pulses generated by movement in one direction relative to the incremental pattern causing the internal counter to count down and UP pulses generated by movement in an opposing direction causing the internal counter to count up;

characterised in that the apparatus further comprises means for generating following origin signals with preset width(P) using software, wherein the origin pattern is actually detected in the first operation alone, and the following origin signals are subsequently generated virtually by software according to the count value of the internal counter (48).
The apparatus for generating origin signals of an encoder according to claim 2, further comprising means for storing an origin position detected by an initial operation after power-on and the preset width(P) of the origin signal.